While I have the option, I decided long ago not to pursue US citizenship.  My biggest concern was having to register for the draft but the tax code in the US is insanely complex and one of the hoops to jump through in order to get my citizenship was to file the 10 previous years of income tax forms.  In my mind, it wouldn't make sense to pursue it unless I were to take up residence there on a permanent basis and I was already comfortable here.

 A friend of my sister is currently going through the process of renouncing her US citizenship and it involves an interview and a hefty processing fee.  She's got a business in Canada and she's been paying US federal income tax every year - she has dual citizenship.  I don't know the specifics of her case but there is a tax treaty between Canada and the US which prevents double taxation on your income so my mom never paid a dime in US taxes while she lived and worked here as a permanent resident.  I guess the difference is employment vs self-employment.